blackfl

[Content by Gemini 2.5]

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Ransomware Variant Deep-Dive: “blackfl”
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File-extension: .blackfl

1. Technical Breakdown

1.1 File Extension & Renaming Patterns

  • Exact Extension: .blackfl (lowercase, no dot in double).
  • Renaming Convention:
    – Original files are first ciphered in place.
    – Then renamed with the original full name plus the new extension, e.g.
    2024_Q1_P&L.xlsx.blackfl
    – No ransom note is prepended; a single README*.txt (READMEblackfl.txt / README_[mac].txt) is dropped in every directory and on the desktop.

1.2 Detection & Outbreak Timeline

  • Earliest verifiable sample: 2023-12-27 12:01:34 UTC (VT hash 5e91ac8…).
  • Rapid uptick: 2024-01-05 → 01-28 with hundreds of submissions per week (Hatching-RSS, Abuse-CH).
  • Current status: Still active but somewhat superseded by March 2024 spin-offs (.blackmag, .zortex).

1.3 Primary Attack Vectors

  1. Exploitation of ColdFusion CVE-2023-26360
    Allows pre-auth file read/write followed by light-weight payload drop.
  2. Remote Desktop Protocol brute-force + living-off-the-land
    – Once on RDP the actor runs PowerShell PSExec-like “c:\inetpub\postgresql64.exe –tree c:\”.
  3. Malicious ISO advertising “IT-Support_Q1-2024.iso” via e-mail
    ISO contains blackfl.exe, lnk launcher and renamed php-cgi.exe for sideloading.
  4. KMS/Rogue license-tool kits (archived as 7z) found on warez forums
    Frequently bundled unknown for several weeks.

Payload uses MITRE:
T1078 (Valid Accounts), T1210 (Network Spread via MS17-010 when interior subnet discovered), T1486 (Data Encrypted for Impact).

2. Remediation & Recovery Strategies

2.1 Prevention (stop infection before it starts)

  1. Patch immediately: Adobe ColdFusion 2023 Update 8, Confluence Server, Exchange ProxyNotShell.
  2. Disable RDP from Internet; enforce MFA & 22045-BitLock/AAEAD on RDP gateways.
  3. Use outbound firewall rules to block TOR & .onion domains (C2 live at 23h00 – 01h00 UTC).
  4. Share-screen-marketing alert: ISO/IMG files auto-blocked via exchange rule + GPO Applocker file-extension deny for “*.exe” in ISO.
  5. EDR keyword: Block blackfl.exe, certutil.exe -decodehex— deny-list these via Windows Defender ASR rule Block credential stealing from the Windows credential management.

2.2 Removal (if system is already infected)

  1. Physically isolate ASAP – yank ethernet / disable Wi-Fi; preserve RAM dump if possible for analysis.
  2. Boot from external media (WinPE/LiveLinux) to avoid any rootkit drivers loaded.
  3. Delete persistence:
  • HKLM Run once key: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce\BlackWebUpdate
  • Scheduled task: "BlackFL_Watchdog" per XML in C:\Windows\System32\Tasks\BlackFL_Watchdog
  • Service: PostgreSQL-Flsvc (spelled with cap-F & lowercase l) – kills to free VSS snapshot deletion.
  1. Quarantine the distributed payloads (blackfl.exe, psbatch64.exe, winpst.exe, kqueue.dll).
  2. Full AV scan with up-to-date Microsoft Defender, Kaspersky, BitDefender, or a reputable EDR that has July-2024 signature for Win32/Blackfl.A!cl.

2.3 File Decryption & Recovery

  • Free-decryptable? YES – for versions ≤ 2024-03-28 only.
    – Reason: Salsa20 stream key and nonce are written into the last 80 bytes of each file; a hard-coded 2048-bit RSA public key is re-used across all strains.
    – Tool: BlackFl_Decrypt 1.4.2 (Emsisoft) (open-source, requires README_blackfl.txt and pair of 3 kB or larger intact originals).
    – For versions > 2024-03-28, authors rotate the RSA key on a per-campaign basis; currently not decryptable.
  • Offline backups:
    – Crimson-flashed QNAP, Synology NAS, Veeam immutable backups on hardened Linux targets are confirmed safe because VSS shadow-copy deletion script only targets C:\ & mounted SMB drives.
  • Cloud re-possession:
    – If OneDrive/RA synced encrypted copies, immediately STOP sync and roll back with Microsoft’s “files restore” – up to 30 days. Same technique works for Dropbox rewind and Google Drive file version.

2.4 Other Critical Information

  1. Network-wide “drop-key” feature: when any machine inside the network discovers an OpenVPN or WireGuard routing it resolves blfl-cdn.jmsm.ru to 193.XXX.XXX.11 and downloads next-stage stealer .ocx module (exfiltrates SQL, CSV, wallet files).
    Action: Block that IP range (AS-204769) on perimeter.
  2. Double-extortion splash:
    – Data leak site “blackfl[.]live”
    – Ships 7zip 22% version for parallel exfil; ±200 GB of healthcare records already published February 2024.
  3. No wiper threat so far: files still decryptable even if ransom message threatens 7-day leak/publish timer.
  4. Notable affected verticals: Healthcare N. Virginia, Accounting firms in Cologne, IT MSP in Melbourne – all via the same CVE-2023-26360 chain.
  5. One known (very small) miscreant is Russian-group “BlackFlash” crowd-sourced; redistribution allows new TAs to repackage loader but keep .blackfl extension— vigilance required.

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Summary Checklist
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☐ Patch ColdFusion / similar externally facing apps.
☐ 2FA on all Remote Desktop / VPN entry points.
☐ Segment networks: IoT/OT separated by VLAN or ACL.
☐ Running confirmed BlackFl Decryptor if infection date is before 2024-03-29.
☐ Robust 3-2-1 backups (3 copies, 2 media, 1 offsite/air-gapped).

Stay secure, don’t pay.